In the MouseDown event handler, see if the point is on one of the points. If so, save the index of the point.

In the MouseMove event handler, move the point to its new location and redraw the line.

In the MouseUp event handler, set m_GrabbedPoint = -1 to indicate that no point is selected.

Private Sub picCanvas_MouseDown(Button As Integer, Shift As _
Integer, X As Single, Y As Single)
Dim i As Integer
' See if this is a point.
m_GrabbedPoint = -1
For i = 0 To 1
' See if the point is within the point.
If Abs(X - m_X(i)) <= GRAB_WID / 2 And _
Abs(Y - m_Y(i)) < GRAB_WID / 2 _
Then
' This is the point.
m_GrabbedPoint = i
Exit For
End If
Next i
End Sub
Private Sub picCanvas_MouseMove(Button As Integer, Shift As _
Integer, X As Single, Y As Single)
' Do nothing if no point is grabbed.
If m_GrabbedPoint < 0 Then Exit Sub
' Save the new coordinates.
m_X(m_GrabbedPoint) = X
m_Y(m_GrabbedPoint) = Y
' Draw the moved point.
DrawLines
End Sub
Private Sub picCanvas_MouseUp(Button As Integer, Shift As _
Integer, X As Single, Y As Single)
m_GrabbedPoint = -1
End Sub